JPH0229937A - Light pickup device - Google Patents

Abstract

PURPOSE:To relax acceleration received from an external part and to improve a tracking servo property by injecting a magnetic fluid into a magnetic circuit part between a magnetic void for control and a coil for control. CONSTITUTION:A magnetic fluid 10 is injected into a void between a focusing coil 7 fitted to the lower cylindrical part of a lens holder 5 and a permanent magnet 3. With a constitution, the magnetic fluid 10 can always stay at the void by the act of a magnetic field, and when strong acceleration is received from and external part, the most part of rapid motion due to the clearance of a holder 5 bearing part and a supporting shaft 4 is absorbed by the viscosity of the magnetic fluid 10. Moreover, since the flux of a magnetic circuit passes through within the magnetic fluid 10, flux density is increased. Consequently, the servo property of a device can be improved inexpensively.

Description

Detailed Description of the Invention [Industrial Utilization Public Expenditure] The present invention relates to an optical pickup device, particularly a playback device or playback device that focuses and tracks a light spot focused on the information recording surface of an optical disc. The present invention relates to an optical pickup device for a recording/reproducing device.

[Conventional technology]

FIG. 2 is a partial cross-sectional view showing the electromagnetic mechanism part of a conventional optical pickup device.
A cylindrical focus control permanent magnet 3 is magnetized in the radial direction and is attached to the inner surface of the outer yoke 1.

Reference numeral 4 designates a support shaft held by the inner peripheral line 2, on which the lens holder 5 is fitted so that it can slide in the direction of arrow A and freely rotate in the direction of arrow B.

An objective lens 6 is fixed to the lens holder 5 at a position a certain distance away from the support shaft 4.

7 is a focusing coil attached to the lower cylindrical portion of the lens holder 5; 8 is a focusing coil attached to the lower cylindrical portion of the lens holder 5;
Tracking coils are mounted symmetrically with respect to the support shaft 4 on the side surfaces of the upper part of the shaft.

Reference numeral 9 denotes a permanent magnet for track control that faces the tracking coil 8 and is radially magnetized into multiple poles along the circumferential direction.

Next, the operation will be explained.

By applying a servo current to the focusing coil, the lens holder 5 slides in the direction of arrow A depending on the polarity of the servo current, changing the distance between the objective lens B and the optical disc (not shown) to perform focusing servo. Further, tracking servo is performed by applying a desired current to the tracking coil 8 and rotating the lens holder 5 in the direction of arrow B.

The light beam from the Z direction is incident on the objective lens 6, and its position is controlled by the focusing servo and tracking servo, and is focused onto the optical disk.

[Problem to be solved by the invention]

Since the conventional optical pickup device is configured as described above, a clearance necessary for sliding and rotation exists between the inner surface of the sliding bearing of the lens holder 5 and the support shaft 4.

When this optical pickup device receives strong acceleration from the outside, the lens holder 5 may make a sudden movement that cannot be converged by the focusing servo or tracking servo due to the above-mentioned clearance. There were problems such as the light beam focusing spot deviating from the information track on the disk, resulting in misreading of information or loss of information.

This invention was made to solve the above-mentioned problems, and it is possible to accurately read information without the optical AMM switch being displaced from the information track on the optical disk even when subjected to strong acceleration from the outside. The purpose of the present invention is to obtain an optical pickup device with excellent servo characteristics.

[Means to solve the problem]

The optical pickup device according to the present invention injects a magnetic fluid into a magnetically equivalent portion between a control magnetic gap that drives a lens holder and a control coil placed therein in order to alleviate strong external acceleration. This is what I did.

[Effect]

In the optical pickup device of this invention, magnetic fluid is injected into the magnetic gap where the drive coil that drives the lens holder is located, so that the lens holder starts to move rapidly when it receives strong acceleration from the outside. However, the magnetic fluid's viscosity eases the glossing motion, allowing the focus servo and tracking servo to function sufficiently, making it possible to accurately read information without causing the optical SM light spot to deviate from the information track on the optical disk. .

〔Example〕

An embodiment of this invention will be described below.

FIG. 1 is a partially enlarged sectional view mainly showing the focusing electromagnetic mechanism of an optical pickup device according to an embodiment of the present invention, and the same members as in FIG. 2 are given the same reference numerals and will be explained. Omitted.

In FIG. 1, 1 is an outer circumferential yoke, 2 is an inner circumferential yoke continuous to the outer circumferential yoke 1, and 3 is a cylindrical permanent magnet for focus control magnetized in the radial direction. 7 is a focusing coil attached to the lower cylindrical part of the lens holder 5,
It is composed of an inner circumferential yoke 2 and a permanent magnet 3 and is located within a magnetic gap. A magnetic fluid 10 is injected into the gap between the focusing coil and the permanent magnet 3.

Next, the operation will be explained.

The basic operation is that when a servo current is supplied to the focusing coil 7, the lens holder 5 slides depending on the polarity of the servo current, changes the distance between the objective lens S and the optical disk (not shown), and the focusing servo is activated. It will be done.

At the same time, when a tracking servo current is applied to a tracking coil (not shown), the polarity of the current causes the lens holder 5 to rotate left and right around the spindle 4, thereby rotating the lens holder 5 in the circumferential direction. Tracking servo can be applied by swinging the servo.

Here, the magnetic fluid 10 is injected into the gap between the focusing coil 7 and the permanent magnet 3 and placed around the entire circumference of the magnetic gap using the magnetic field formed by the inner yoke 2, the outer yoke 1 continuous thereto, and the permanent magnet 3. are doing.

The magnetic fluid 10 can always remain in this magnetic gap due to the action of the magnetic field, and since it is a fluid, it can have an appropriate viscosity.

In the case of the optical pickup device shown in Fig. 1, when it receives strong acceleration from the outside, it starts to move suddenly because there is a clearance between the bearing part of the lens holder 5 and the support shaft 4. The portion is absorbed and relaxed by the viscosity of the magnetic fluid 10, and the movement of the lens holder 5 is focused and
Tracking co-control is relaxed to the level where it works, and it is possible to obtain servo characteristics that are the same as when there is no disturbance.
Misreading of information on an optical disk and omission of read information are less likely to occur.

〔Effect of the invention〕

As described above, according to this invention, since the magnetic fluid is injected into the magnetic gap formed by the control permanent magnet, the fluid can always be held at the same position, and the lens holder coil Since the part is in contact with this magnetic fluid, the viscosity of the fluid can alleviate the impact of disturbances.Furthermore, since the magnetic flux of the magnetic circuit passes through the magnetic fluid, the magnetic flux density increases and the servo mechanism It has the effect of improving sensitivity, and also being able to transfer and dissipate heat generated by the coil to the magnet side, and has the effect that the servo characteristics of the optical pickup device can be improved at a lower cost overall.

[Brief explanation of the drawing]

FIG. 1 is an enlarged partial cross-sectional view of the 7-focusing electromagnetic mechanism of an optical pickup device according to an embodiment of the present invention, and FIG. 2 is a partial cross-sectional view of a conventional optical pickup device. be. In the figure, 1 is an outer yoke, 2 is an inner yoke, 3 is a permanent magnet, 4 is a spindle, 5 is a lens holder, 6 is an objective lens,
7 is a focusing coil, 8 is a tracking coil,
9 indicates a permanent magnet, and 10 indicates a magnetic fluid. Note that the same reference numerals in the figures indicate the same or corresponding parts. Agent Masuo Oiwa (2 others)

Claims (1)

[Claims] In an optical pickup device that includes a lens holder that holds an objective lens, and a drive device that drives the lens holder to focus and track a light spot that is focused on a disk via the objective lens, a control magnetic air gap is provided. An optical pickup device characterized in that a magnetic fluid is injected into a magnetic circuit between the control coil and the control coil arranged in the air gap.